In-ear monitors, also referred to as canal phones and stereo headphones, are commonly used to listen to both recorded and live music. A typical recorded music application would involve plugging the monitor into a music player such as a CD player, flash or hard drive based MP3 player, home stereo, or similar device using the monitor's headphone jack. Alternately, the monitor can be wirelessly coupled to the music player. In a typical live music application, an on-stage musician wears the monitor in order to hear his or her own music during a performance. In this case, the monitor is either plugged into a wireless belt pack receiver or directly connected to an audio distribution device such as a mixer or a headphone amplifier. This type of monitor offers numerous advantages over the use of stage loudspeakers, including improved gain-before-feedback, minimization/elimination of room/stage acoustic effects, cleaner mix through the minimization of stage noise, increased mobility for the musician and the reduction of ambient sounds.
In-ear monitors are quite small and are normally worn just outside the ear canal. As a result, the acoustic design of the monitor must lend itself to a very compact design utilizing small components. Some monitors are custom fit (i.e., custom molded) while others use a generic “one-size-fits-all” earpiece.
Prior art in-ear monitors use either diaphragm-based or armature-based receivers. Broadly characterized, a diaphragm is a moving-coil speaker with a paper or mylar diaphragm. Since the cost to manufacture diaphragms is relatively low, they are widely used in many common audio products (e.g., ear buds). In contrast to the diaphragm approach, an armature receiver utilizes a piston design. Due to the inherent cost of armature receivers, however, they are typically only found in hearing aids and high-end in-ear monitors.
Diaphragm receivers, due to the use of moving-coil speakers, suffer from several limitations. First, because of the size of the diaphragm assembly, a typical earpiece is limited to a single diaphragm. This limitation precludes achieving optimal frequency response (i.e., a flat or neutral response) through the inclusion of multiple diaphragms. Second, diaphragm-based monitors have significant frequency roll off above 4 kHz. As the desired upper limit for the frequency response of a high-fidelity monitor is at least 15 kHz, diaphragm-based monitors cannot achieve the desired upper frequency response while still providing accurate low frequency response.
Armatures, also referred to as balanced armatures, were originally developed by the hearing aid industry. This type of driver uses a magnetically balanced shaft or armature within a small, typically rectangular, enclosure. As a result of this design, armature drivers are not reliant on the size and shape of the enclosure, i.e., the ear canal, for tuning as is the case with diaphragm-based monitors. Typically, lengths of tubing are attached to the armature which, in combination with acoustic filters, provide a means of tuning the armature. A single armature is capable of accurately reproducing low-frequency audio or high-frequency audio, but incapable of providing high-fidelity performance across all frequencies. To overcome this limitation, armature-based in-ear monitors often use two, or even three, armature drivers. In such multiple armature arrangements, a crossover network is used to divide the frequency spectrum into multiple regions, i.e., low and high or low, medium, and high. Separate armature drivers are then used for each region, individual armature drivers being optimized for each region. Unfortunately, as armatures do not excel at low-frequency sound reproduction, even in-ear monitors using multiple armatures may not provide the desired frequency response across the entire audio spectrum. Additionally, the costs associated with each armature typically prohibit the use of in-ear monitors utilizing multiple armature drivers for most applications.
Although a variety of in-ear monitors have been designed, these monitors do not provide optimal sound reproduction throughout the entire audio spectrum. Additionally, those monitors that achieve even a high level of audio fidelity are prohibitively expensive. Accordingly, what is needed in the art is an in-ear monitor that achieves the desired response across the audio spectrum at a reasonable cost. The present invention provides such a monitor.